The present invention relates to a hydraulic control arrangement. More particularly, it relates to a hydraulic control arrangement for a working device which is driven by a hydromotor and especially arranged on agricultural vehicles.
Such proportional operating control arrangements are known in the art. One of such control arrangements is disclosed for example, in the DE-OS No. 3,318,052. In this control arrangement a control slider for controlling a single-working power lift is formed as a pressure compensating valve and a pressure reducing throttle valve, and the power lift is secured by a blocking unit. This control arrangement operates in a manner of close circuit and provides a load pressure compensating control. It has however the disadvantage that a control conduit which branches from the control slider extends through a control chamber which lies between a first working chamber associated with pressure medium stream which flows to the power lift and a discharge chamber which is associated with pressure medium stream flowing out of the power lift to the tank. The control conduit extends in the housing downstream of the control chamber via a pressure subdividing circuit of two throttle points and via a return chamber to the tank. Because of this control oil stream, the above described control arrangement for closed circuit cannot use the housing which is used in similar control arrangements for open circuits.
Another control arrangement is proposed in the German Patent Application No. P 3,431,103 which is formed for an open circuit and whose control slider cooperates with a three way throttle slider. In this control arrangement the control oil stream which branches upstream of the control slider is supplied via a spring chamber on the throttle slider and then via a control chamber of the control slider. This control chamber is located between a second working chamber and a second return chamber. Thereby it is possible in this control arrangement to provide advantageous operation in that, for example, in lowering position the control pressure for unblocking of the blocking unit can be lifted and only a control oil stream in the lowering position is required, and the energy losses in the neutral position are small because of low circulating pressure. The disadvantage of this control arrangement is that while it has its inherent advantage, it cannot be used for a type with closed circuit.